To cope with the increasing demand for wireless data traffic after commercialization of 4G communication systems, active efforts are underway to develop enhanced 5G or pre-5G communication systems. As such, 5G or pre-5G communication systems are referred to as beyond 4G communication systems or post LTE systems. To achieve high data rates, use of the extremely high frequency (mmWave) band (e.g. 60 GHz band) is expected in a 5G communication system. To reduce propagation pathloss and to increase propagation distance at the mmWave band, use of various technologies such as beamforming, massive MIMO, full dimensional MIMO (FD-MIMO), array antenna, analog beamforming and large scale antenna are under discussion for 5G communication systems. To enhance system networks, various technologies such as evolved or advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP) and interference cancellation are under development for 5G communication systems. In addition, for 5G communication systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) are under development for advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) are under development for advanced access.
Meanwhile, the Internet is evolving from a human centered network where humans create and consume information into the Internet of Things (IoT) where distributed elements or things process and exchange information. Big data processing through cloud servers and IoT technology are being combined into the Internet of Everything (IoE). To realize IoT services, base technologies such as sensing, wired/wireless communication and network infrastructure, service interfacing and security are needed, and technologies interconnecting things such as sensor networks, Machine-to-Machine (M2M) or Machine Type Communication (MTC) are under development. In IoT environments, it is possible to provide intelligent Internet technology services, which collect and analyze data created by interconnected things to add new values to human life. Through convergence and combination between existing information technologies and various field technologies, IoT technology may be applied to various areas such as smart homes, smart buildings, smart cities, smart or connected cars, smart grids, health-care, smart consumer electronics, and advanced medical services.
Accordingly, various attempts are being made to apply 5G communication systems to IoT networks. For example, sensor networks and machine-to-machine or machine type communication are being realized by use of 5G communication technologies including beamforming, MIMO and array antennas. Application of cloud RANs to big data processing may be an instance of convergence of 5G communication technology and IoT technology.
In recent years, with rapid advances in wireless communication technologies, mobile communication systems have evolved across generations. Currently, the long term evolution (LTE) system attracts attention as a fourth generation mobile communication technology. To meet explosive growth in traffic demand, various techniques including carrier aggregation (CA) have been introduced to the LTE system. In most cases, a single carrier is used in communication between a user equipment (UE) and a base station (eNB). When carrier aggregation is employed, a primary carrier and one or more secondary carriers may be used in communication between a user equipment (UE) and a base station (ENB), significantly increasing the data transfer rate by an amount corresponding to the number of secondary carriers. In LTE, the primary carrier is termed a primary cell (PCell), and a secondary carrier is termed a secondary cell (SCell). A CA-capable UE may connect to a single PCell and up to four SCells.
The LTE system is a communication system that originally operates in a licensed frequency band allocated by the government. Recently, to meet explosive growth in traffic demand, an active discussion is under way about the use of the LTE technology in the unlicensed frequency band, which is currently used for wireless LANs, Bluetooth, and the like. This is referred to as Licensed-Assisted Access (LAA) to unlicensed spectrum.
To combine carrier aggregation with LAA, it is possible to consider a scenario where the PCell uses a licensed band frequency and the SCell uses an unlicensed band frequency on the basis of LAA.
However, the unlicensed band is already populated by different types of systems such as Wi-Fi and Bluetooth. While a UE is using a Wi-Fi network operating at a specific frequency of the unlicensed band, when an LTE ENB configures the UE with an LAA cell operating at the same unlicensed band frequency, it may be not possible to simultaneously utilize the two technologies at the same frequency.